The present invention relates to novel uranium compounds, a process for the preparation thereof and their use as catalysts for the hydrogenation of unsaturated organic compounds, particularly olefins.
Olefin hydrogenation processes usually use heterogeneous catalysis and hydrogenation catalysts based on precious metals on inert supports.
Although these heterogeneous catalysis processes are widely used industrially and give good results, there is now a significant interest in homogeneous catalysis methods using soluble complexes for finding solutions to hydrogenation problems necessitating a certain selectivity.
Thus, the mechanisms occurring in homogeneous catalysis involves interactions between the olefin and a metal within a dissolved complex, and the nature of the metal as the structure of the complex are determinative elements for the development of the reaction. Generally, the metals used in these complexes are series d transmission metals, particularly metals of the platinum and palladium series. However, the use of such metals is disadvantageous due to their very high price and their scarceness.
Consideration has also been given to the use of other metals and for some years now there has been considerable interest in uranium compounds with a low degree of oxidation, because it has been found that, although the properties of uranium are far removed from those of precious metals, certain uranium III compounds have an affinity for olefins, as is described in the article in J. CHEMICAL, Soc., Chem. Commun, 1982, pp. 323/4.
Moreover, uranium is very easy to work up, is very inexpensive in the depleted state and is available in a very pure form, because the nuclear industry requires a high degree of purity.
However, this affinity is not observed for all uranium III compounds, e.g. in the case of compound (C.sub.5 H.sub.5).sub.3 U.
In the same way, the standard uranium compounds such as (C.sub.5 H.sub.5).sub.3 UCH.sub.3, (C.sub.5 H.sub.5).sub.3 UCl and (C.sub.8 H.sub.8).sub.2 U do not interact with the molecules to be activated, because they are either too stable, or are coordination number saturated. Other uranium compounds have also been investigated which are more difficult to prepare as a result of their instability, particularly trivalent uranium derivatives, which are soluble in organic solvents, which is not the case with uranium derivatives of type (C.sub.5 H.sub.5).sub.3 U.